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Thread: Help, please

  1. #1
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    Unhappy Help, please

    I have a little problem with my 1991 k75, had this bike since new and never have problems till now, the engine starts and runs nice and easy but, after half mile down the road, engine starts missing and sometimes it quits running and back fires, I checked the fuel pump and it works, I cleaned fuel filter and put fresh fuel and still the same problem, anyone knows what the problem may be ?
    Thanks, Frank.

  2. #2
    Could it be a magnetic pick-up (if the 1991s have one). When they get hot they can beak the circuit and the engine dies. Let the engne cool down and they start up again like nothing has happened.

  3. #3
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    Magnetic pick up ???

    Quote Originally Posted by RJM2096 View Post
    Could it be a magnetic pick-up (if the 1991s have one). When they get hot they can beak the circuit and the engine dies. Let the engne cool down and they start up again like nothing has happened.
    What is a magnetic pick up ?, never heard of this term.

  4. #4
    BUDDINGGEEZER
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    Hall sensor. Clymer calls it the Hall transmitter unit. It is under the t shape cover on the front of the engine. remove cover and heat sensor with a hair dryer, engine running. If the engine misses or dies when it is heated, it's bad. Around $500 new, but used ones can be found.

    Ralph Sims

  5. #5
    What, me worry? GILLY's Avatar
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    I think he's talking about the ignition control unit.

    My thought on reading your first post, is HOW do you CLEAN the fuel filter? If you don't know how old it is I'd put a new one is as a matter of course. In other words it SHOULD be done every 2 or 3 years anyways, so toss one in and see if it fixes it.

    I'm sure one of our K BIke experten will be along shortly

    Gilly
    87 K75S, bought new, now sold
    07 K1200GT Bought new, now traded in
    13 C650GT
    MOA 44606

  6. #6
    A bozo on the bus deilenberger's Avatar
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    The ignition trigger (Hall-Effect-Sensor) is certainly a possibility.. but before doing the test on it (good one described above by Ralph Sims - called the "Dunkle" test after Jeff D who first came up with it..) I'd look at a few more things, and need some more info:

    1 - When it the last time the bike got new plugs?
    2 - What's happening on the instrument panel, especially the lights, when this happens?

    And I'd agree about just putting a new fuel filter in (although they have gotten just a tad pricey now.. so I can understand the reluctance there..)
    Don Eilenberger http://www.eilenberger.net
    Spring Lk Heights NJ NJ Shore BMW Riders
    '12 R1200R - I love this bike!

  7. #7
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    Thanks guys..

    Quote Originally Posted by BuddingGeezer View Post
    Hall sensor. Clymer calls it the Hall transmitter unit. It is under the t shape cover on the front of the engine. remove cover and heat sensor with a hair dryer, engine running. If the engine misses or dies when it is heated, it's bad. Around $500 new, but used ones can be found.

    Ralph Sims
    That is a good way to test it, Thanks. And about the fuel filter, I just bypassed it, of course I will install a new one,
    Spark plugs are new and nothing different on the dash lights, Thank you guys I do appreciate your help. Frank.

  8. #8
    Chairman of the hoard wmubrown's Avatar
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    Trace your steps backwards... just prior to this happening, did you do ANYTHING to the bike? Wash it? Change those old spark plugs? Anything? Always double check your work - that the new spark plugs are gapped properly, that the plug boots snapped on solidly, etc. Start simple (sounds like you have - fuel filter, etc) and start with the most recent work done.
    John A. Brown - Kalamazoo MI
    '09 K1300S 'Zoot' (Wicked, bad, naughty, evil, Zoot!)
    '94 K1100LT 'Desert' (the horse with no name)

  9. #9
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    Good idea..

    Quote Originally Posted by wmubrown View Post
    Trace your steps backwards... just prior to this happening, did you do ANYTHING to the bike? Wash it? Change those old spark plugs? Anything? Always double check your work - that the new spark plugs are gapped properly, that the plug boots snapped on solidly, etc. Start simple (sounds like you have - fuel filter, etc) and start with the most recent work done.
    Thanks for the note, as a matter of fact I did change the rear seal on the engine and had to remove the transmition, also I disconeted some electrical items, I will be checking everything again, Thanks.

  10. #10
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    What spark plugs are you using? I went from the BMW OEM Bosch to NGKs and after a little bit I had a miss every now and again. I decided to take a look at the plugs and the one in the 3rd cylinder was destroyed! Needless to say I am back to Bosch plugs.

  11. #11
    This problem screams "water in the fuel." It settles into the low sump beneath the fuel pump and sits there with the bike stationary. After it jostles around a bit in that first mile or so droplets get picked up by the pump. Which causes anything from a misfire to the bike quits. After the water settles back out it gets good gas for a little while, so restarts. Repeat! That is my take on the issue.

    That is not the only possible cause - but it seems more likely than an electronic one to me because electronics that go wonky usually take more than a mile or so to warm up enough to fail. Usually!

    Next time it acts up check for spark at the spark plugs. I do a quick check with a timing light. Clip the inductor around a plug wire and shine the light onto a surface where I can see if it is flashing, and flashing regularly.
    Paul Glaves - "Big Bend", Texas U.S.A
    "The greatest challenge to any thinker is stating the problem in a way that will allow a solution." - Bertrand Russell
    http://web.bigbend.net/~glaves/

  12. #12
    What, me worry? GILLY's Avatar
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    Quote Originally Posted by toddlamp View Post
    What spark plugs are you using? I went from the BMW OEM Bosch to NGKs and after a little bit I had a miss every now and again. I decided to take a look at the plugs and the one in the 3rd cylinder was destroyed! Needless to say I am back to Bosch plugs.
    I can't say this for every year or even every bike (these manufacturers will switch on ya) but my 87 had BERU as the OEM plug. I switched to Bosch and had an immediate problem (crack in an area I didn't even think they had business making a joint to leak to begin with! Between the threads and "hex" shape), so a local non-BMW dealer tryed NGK and was happy with those plugs from then on.
    87 K75S, bought new, now sold
    07 K1200GT Bought new, now traded in
    13 C650GT
    MOA 44606

  13. #13
    Quote Originally Posted by 55960 View Post
    What is a magnetic pick up ?, never heard of this term.
    Sorry I am use to calling up parts stores and asking for a magnetic pickup. BMW uses the more official word Hall-Effect Sensor.


  14. #14
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    Quote Originally Posted by RJM2096 View Post
    Sorry I am use to calling up parts stores and asking for a magnetic pickup. BMW uses the more official word Hall-Effect Sensor.

    That photo is not it. In the fische they call it an ignition sensor.

    http://www.maxbmwmotorcycles.com/fic...p?mospid=47908

    Click on 12-Engine Electrics.
    Then on ignition sensor.

    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

    Lee Fulton Forum Moderator
    3 Marakesh Red K75Ss
    Mine, Hers, Spare

  15. #15
    I think I'd throw a bottle of HEET into the tank. It's about a buck and may just solve your problem. It will also dissolves some of the gunk in your tank and injectors. If the HEET doesn't solve it, then do the plugs. Go to your favorite parts store and get a set of Bosch or get them to cross reference and find a set of cheap Champions (usually only a couple of bucks and work pretty good). If that doesn't solve it, then look at the Hall Effect sensor.

    Always begin with the simple things first. You were thinking of the easy fixes when you bypassed the filter, but if there was water in the gas, it would have made it through the pump, along with any gunk in the tank, to the injectors and could still be gumming up the injectors. I don't ever run straight gas from the tank because of the accumulation of gunk.

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